1. Field of the Invention
The present invention relates to a butterfly damper for a loudspeaker, and especially to a high-input type butterfly damper.
2. Description of the Related Art
The conventional butterfly damper 7 has an inner circumferential frame 9, an outer circumferential frame 8 and arm members 10 for connecting the inner circumferential frame 9 and the outer circumferential frame 8 to each other, as shown in FIG. 5. A voice coil is inserted into the inner circumferential frame 9. The outer circumferential frame 8 is fixed to the other structural component (for example, a framework of the loudspeaker). Excitation of the voice coil causes the inner circumferential frame 9, which is supported by means of the arm members 10 having flexibility, to vibrate together with the voice coil.
The conventional butterfly damper 7 is formed utilizing the injection forming so that the arm member 10 and the outer circumferential frame 8 are connected to each other to form a flush surface, taking into consideration simplification of the parts and facilitation of the injection forming. More specifically, the arm member 10 and the outer circumferential frame 8 are connected to each other so that the upper surface 8a of the outer circumferential frame 8 is flush with the upper surface 10a of the arm member 10, as shown in FIG. 6.
The conventional butterfly damper 7 however has a problem that amplitude increased by inputting a high input signal causes stress concentration in the arm member 10, resulting in a state in which the arm member 10 is not able to bear the stress, leading to its breakage or occurrence of rupture. The conventional butterfly damper 7 is not adaptable to the high input signal in this manner.
Stress tends to concentrate on the connecting portion of the arm member 10 to the outer circumferential frame 8, and more specifically on the portion of the connecting portion, which has a small curved surface.
An object of the present invention is therefore to provide a butterfly damper, which has a shape feature by which stress can be distributed and reduced, thus permitting to bear a high input signal.
In order to attain the aforementioned object, a butterfly damper according to the first aspect of the present invention comprises:
an inner circumferential frame;
an outer circumferential frame having opposite end surfaces and an inner peripheral surface, said inner peripheral surface being connected to said opposite end surfaces to form opposite connecting edge portions; and
at least one arm member having one end connected to said outer circumferential frame and an other end connected to said inner circumferential frame,
wherein:
said one end of said at least one arm member is connected to a portion of said inner peripheral surface of said outer circumferential frame, said portion excluding said opposite connecting edge portions.
According to the first aspect of the present invention, the one end of the at least one arm member is connected to a portion of the inner peripheral surface of the outer circumferential frame, which excludes the opposite connecting edge portions. Even when operation of the damper causes the inner circumferential frame to oscillate, the above-mentioned portion of the inner peripheral surface of the outer circumferential frame serves as a blocking wall for preventing the arm member from oscillating excessively, thus reducing stress.
In the second aspect of the present invention, each of the one end and the other end of the at least one arm member may have at least one curved surface. According to the second aspect of the present invention, the curved surface is formed at each of the opposite ends of the arm member, which connects the inner circumferential frame and the outer circumferential frame to each other, in the vicinity of which stress concentration tends to occur. It is therefore possible to distribute stress, which is to be applied to the adjacent portion of the arm member as connected, to the end thereof, thus reducing the load of stress.
In the third aspect of the present invention, a plurality of arm members may be provided as the at least one arm member. According to the third aspect of the present invention, it is possible to make a change in length, width and the other conditions of the arm member to the optimum values in accordance with a level of an input signal value and a size of the butterfly damper. Selection of the appropriate values for these conditions may lead to variation in the number of the arm members. There is no limitation in the number of the arm members.
In the fourth aspect of the present invention, the inner circumferential frame, the outer circumferential frame and the at least one arm member may be formed of resin integrally with each other by an injection forming. According to the forth aspect of the present invention, utilizing the injection forming makes it possible to manufacture the integrally-formed butterfly damper in an easy manner. In the present invention, change in shape of the damper suffices to improve only performance of it without increasing a cost.